The present invention relates to improvements in internally heated or cooled rotary units which can constitute the cylinders of calenders or analogous machines, and more particularly to improvements in rotary units of the type wherein a fluid heat exchange medium is caused to flow between the internal surface of the cylindrical shell or sleeve of a hollow roller-shaped first component and the exterior of a displacing component or torpedo which is inserted into the interior of the sleeve. Still more particularly, the invention relates to improvements in rotary units wherein the end portions of the sleeve or shell are connected with trunnions and the heat exchange medium enters the interior of the first component by way of one trunnion to leave the first component by way of the other trunnion or wherein the heat exchange medium enters and leaves the first component by way of one and the same trunnion.
It was already proposed to install in the interior of a hollow roller an elongated tubular displacing component and to convey the heat exchange medium through an annular clearance between the internal surface of the shell or sleeve of the roller and the external surface of the displacing component. Spent heat exchange medium can be conveyed into the interior of the displacing component and evacuated from the displacing component by way of that trunnion which admits fresh heat exchange medium. In a presently known construction, one end of the displacing component is secured to one of the trunnions and the other end of the displacing component carries projections which abut against the other trunnion. If the roller is to be heated from within, the displacing component (whose mass is relatively small) expands prior to expansion of the bulkier roller. This is the case when the roller is used to apply pressure to a web of paper which passes through a calender. In such machines, the roller must withstand pronounced deforming stresses and, therefore, its shell or sleeve is thick so that it can withstand high bending or flexing forces. As a rule, the heat-induced expansion of the displacing component is much more pronounced than the heat-induced expansion of the roller when the heating operation begins, i.e., when a stream of hot gaseous or hydraulic fluid begins to flow into the interior of the roller. The differences between the extent of heat-induced expansion of the roller on the one hand and the extent of heat-induced expansion of the displacing component on the other hand can cause damage to the roller and/or other inconveniences. In the aforediscussed conventional construction, that end of the displacing component which is not fixedly secured to the adjacent trunnion is slidably guided in the neighboring portion of the shell. To this end, the unconnected end of the displacing component carries projections which are slidable in the roller. Such construction does not permit for radial expansion of the displacing component with respect to the roller except if the initial mounting of the displacing component is such that the projections are spaced apart from the internal surface of the shell. Loose mounting of the displacing component is undesirable because, once the temperature of the roller matches the temperature of the displacing component, the clearances between the projections and the shell reappear so that the respective end portion of the displacing component is free to perform stray (radial) movements with respect to the roller. This results in repeated contact between the displacing component and the roller with attendant vibrations, noise and other undesirable effects including premature destruction of the displacing component.
The problems which arise as a result of the ability of an end portion of the displacing component to move radially with respect to the roller are aggravated if the roller is very long, if the outer diameter of the roller is large and/or if the difference between the temperature of the displacing component and the temperature of the roller is very pronounced. Such situation can arise in the cylinders of modern supercalenders for treatment of paper webs wherein the length of a calender roller is approximately 8 meters and its outer diameter is approximately 500 mm. The rollers are driven at a peripheral speed of 500 m/min, and the temperature of the heat exchange medium is in excess of 100.degree. C.